Yield and Quality Response of Perennial Ryegrass Selected for High Concentration of Water-Soluble Carbohydrate to Nitrogen Application Rate

The expression of elevated water-soluble carbohydrate (WSC) concentrations in perennial ryegrass (Lolium perenne L.) cultivars selected for high forage WSC concentration can be highly variable across environments. Our aim was to determine whether N application rate influences the expression of the high WSC phenotype. Cultivars AberDart (selected for high WSC concentration) and Fennema (control) were evaluated across four fertilizer N application rates (0, 40, 80, and 120 kg ha(-1) per harvest) over four replicates and 2 yr at Grange, Ireland, and Saerheim, Norway. Plots were managed for silage production with four cuts per year in Ireland and three cuts per year in Norway. Nine forage traits were measured: WSC, dry matter digestibility, crude protein, buffering capacity, dry matter, ash, dry matter yield, N use efficiency, and apparent N recovery. The response of AberDart and Fennema to N application rate was predominantly similar within and over years and locations for all traits. Differences between cultivars in WSC concentration were largely consistent across N application rates, years, and locations. AberDart had mean WSC concentrations 8 to 12% higher than Fennema depending on harvest. Present results suggest that the evaluation and selection of perennial ryegrass for high concentrations of WSC in cool-temperate maritime climates may be conducted across a wide range of N application rates and, by extension, soil N supply rates.